With synchrotron radiation

Ultraviolet photoelectron spectroscopy (UPS) is a variety of photoelectron spectroscopy that is aimed at measuring the valence band, as described in sectionBl.25.2.3. Valence band spectroscopy is best perfonned with photon energies in the range of 20-50 eV. A He discharge lamp, which can produce 21.2 or 40.8 eV photons, is commonly used as the excitation source m the laboratory, or UPS can be perfonned with synchrotron radiation. Note that UPS is sometimes just referred to as photoelectron spectroscopy (PES), or simply valence band photoemission. 

Flimpsel F J, McFeely F R, Morar J F, Taleb-lbrahimi A and Yarmoff J A 1990 Core level spectroscopy at silicon surfaces and interfaces Proc. Enrico Fermi School on Photoemission and Adsorption Spectroscopy and Interfaces with Synchrotron Radiation vo course CVIII, eds M Campagna and R Rose (Amsterdam Elsevier) p 203... 

Typically a few pm but material dependent mono-layer sensitivity with synchrotron radiation... 

Material dependent, but "3% in a two phase mixture with synchrotron radiation can be -0.1%... 

Figure 2 Molybdenum K-edge X-ray absorption spectrum, ln(i /i ) versus X-ray energy (eV), for molybdenum metal foil (25- jjn thick), obtained by transmission at 77 K with synchrotron radiation. The energy-dependent constructive and destructive interference of outgoing and backscattered photoelectrons at molybdenum produces the EXAFS peaks and valleys, respectively. The preedge and edge structures marked here are known together as X-ray absorption near edge structure, XANES and EXAFS are provided in a new compilation of literature entitled X-rsy Absorption Fine Structure (S.S. Hasain, ed.) Ellis Norwood, New York, 1991.

Resonant y-ray absorption is directly connected with nuclear resonance fluorescence. This is the re-emission of a (second) y-ray from the excited state of the absorber nucleus after resonance absorption. The transition back to the ground state occurs with the same mean lifetime t by the emission of a y-ray in an arbitrary direction, or by energy transfer from the nucleus to the K-shell via internal conversion and the ejection of conversion electrons (see footnote 1). Nuclear resonance fluorescence was the basis for the experiments that finally led to R. L. Mossbauer s discovery of nuclear y-resonance in ir ([1-3] in Chap. 1) and is the basis of Mossbauer experiments with synchrotron radiation which can be used instead of y-radiation from classical sources (see Chap. 9). 

In this chapter, we present the principles of conventional Mossbauer spectrometers with radioactive isotopes as the light source Mossbauer experiments with synchrotron radiation are discussed in Chap. 9 including technical principles. Since complete spectrometers, suitable for virtually all the common isotopes, have been commercially available for many years, we refrain from presenting technical details like electronic circuits. We are concerned here with the functional components of a spectrometer, their interaction and synchronization, the different operation modes and proper tuning of the instrument. We discuss the properties of radioactive y-sources to understand the requirements of an efficient y-counting system, and finally we deal with sample preparation and the optimization of Mossbauer absorbers. For further reading on spectrometers and their technical details, we refer to the review articles [1-3]. 

The work of Wortmann et al. [65-67], Gavriliuk et al. [68, 69] and Sturhahn et al. [70] convincingly demonstrates the power of nuclear resonant scattering experiments with synchrotron radiation for high-pressure smdies of magnetism and lattice dynamics. An illustrative example was presented at the Fifth Seeheim Workshop by Wortmann [65] Fig. 9.28a shows NFS spectra of LuFe2 at 295 and... 

Table 8.54 indicates the main characteristics of X-ray powder diffraction. Powder samples of lmg or greater can be analysed. The principal advantage is that substances (e.g. BaS04) can be identified directly, and not indirectly via their elements (e.g. Ba and S). This is particularly advantageous if both silica and silicates (kaolin, talc) are present. Detection limits are matrix dependent, but ca. 3% in a two-phase mixture, with synchrotron radiation ca. 0.1 %. 

More and more radiation sources are switching from discontinuous mode to top-up mode. This means that the user is continuously supplied with synchrotron radiation of almost constant intensity. The loss of the electron current is either compensated continuously or in intervals of several hours (at the ESRF 6 h). 

Topsee and coworkers—in situ XRD synchrotron studies indicate well-dispersed metallic Cu particles upon activation ZnO observed to strain Cu particles by EELS. Topsoe and coworkers,264 utilizing in situ XRD with synchrotron radiation, demonstrated that the Cu phase transforms primarily to a crystalline metallic Cu phase from CuO precursor during activation. Smaller particles were detected when the ternary A1203 component was present (9.5 nm versus 14 nm for the binary Cu/Zn catalyst), indicating that alumina acts primarily as a structural stabilizer, a spacer for well-dispersed Cu particles, which assists in minimizing sintering. 

Mommsen, H., Beier, Th., Dittmann, H., et al. (1996). X-ray fluorescence analysis on inks and papers of incunabula with synchrotron radiation. Archaeometry 38 347-357. 

Except for in house preliminary studies, the intensities of X-rays diffracted by hydrogenase crystals are now usually obtained with synchrotron radiation (Fig. 6.2) and detected by image plate or charge coupled device (CCD) detectors. To limit the damage induced by the powerful photon flux of synchrotrons, the crystals are usually mounted in a small loop, flash cooled in either liquid propane or nitrogen and stored... 

Apphcatiorts of double-crystal topography with synchrotron radiation are dealt with in the next chapter. Here, we cortline otrrselves to laboratory-based apphcatiorts. 

Narayan, R. and Ramaseshan, S. (1981). Optimum choice of wavelengths in the anomalous scattering technique with synchrotron radiation. Acta Crystallogr. A 37, 636-641. 

Helliwell, J. 1. (1990). Macromolecular Crystallography with Synchrotron Radiation. Cambridge University Press, Cambridge. 

As an example let us consider the pentacene/samarium interface (Koch et al, 2002). Samarium has a low work function ((/>m — 2.7 eV), which is comparable to E a from pentacene (— 2.7 eV). Thus, if A 0, the condition Ep, should provide efficient electron injection because in this case fp and LUMO are nearly aligned. In order to avoid contamination that may alter the instrinsic m, h and homo values, such heterostructures have to he prepared in ideally clean conditions, imposing the use of UHV. The UPS experiments performed with synchrotron radiation are shown in Fig. 4.24. After measuring (pM of the clean samarium surface (2.7 eV) as described above, increasing amounts of pentacene are controllably deposited onto the samarium surface. The survey spectra of the valence states and a close-up view of the energy region near E are shown in Figs. 4.24(a) and (b). 

Ito, T. Vacuum ultraviolet photobiology with synchrotron radiation. In Sweet, R.M. Woodhead, A.D. Synchrotron Radiation in Structural Biology. Plenum Publishing Corporation, 1989 221-241 pp. 

Hieda, K. Ito, T. Radiobiological experiments in the X-ray region with synchrotron radiation. Elsevier Science Publishers B. V. Amsterdam, 1991 Vol. 4. 

Munakata, N. Hieda, K. Kobayashi, K. Ito, A. Ito, T. Action spectra in ultraviolet wavelengths (150-250 nm) for inactivation and mutagenesis of Bacillus subtilis spores obtained with synchrotron radiation. Photochem. Photobiol. 1986, 44 (3), 385-390. 

Munakata, N. Saito, M. Hieda, K. Inactivation action spectra of Bacillus subtilis spores in extended ultraviolet wavelengths (50-300 nm) obtained with synchrotron radiation. Photo-chem. Photobiol. 1991, 54 (5), 761-768. 

Nuclear Condensed Matter Physics with Synchrotron Radiation Basic Principles, Methodology and Apphcations... 

The computational effort is larger in ARUPS than in LEED, since more physical processes are involved, so that for the limited purpose of surface crystallography LEED seems more appropriate. Furthermore, ARUPS is best done with synchrotron radiation, which limits its availability. 

Hollinger et al (1985) have studied bronzes NaxW03 and Na2TayW1 y03 near the metal-insulator transition using photoelectron spectroscopy with synchrotron radiation. The results show that the transition is due to localization in an impurity band in a pseudogap. 

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